The present invention relates to catalytic converters and, more particularly, to combined hydrocarbon and ozone converters (CHOC).
Environmental control systems (ECS) may receive compressed air, such as bleed air from a compressor stage of an aircraft. The ECS may cool and condition the bleed air for use in the aircraft cabin and cockpit.
Toxic ozone in the bleed air may become an issue when the aircraft is cruising at altitudes that exceed 20,000 feet. Ozone (O3) is an allotropic form of oxygen and is much more active chemically than ordinary oxygen (O2). It is formed photochemically from oxygen in the Earth's atmosphere and is normally present at high altitudes. To reduce the ozone to a level within satisfactory limits, such as below FAA limits, the ECS may include an ozone-destroying catalytic converter.
Hydrocarbons in the bleed air also may become an issue as they may be odorous and unpleasant for passengers and crew. Odors in aircraft cabins frequently result from ground operations. While an airplane is in the taxi line, exhaust from other airplanes may be ingested into the bleed air system. Hydrocarbons present in bleed air also may include aviation lubricant fumes, hydraulic fluid, and engine exhaust. Hydrocarbons from refueling operations, de-icing operations and ground vehicle exhaust also may be ingested into the bleed air system. To reduce odors, the ECS may include a catalytic converter that converts the hydrocarbons into carbon dioxide and water.
Aircraft have used CHOC to convert ozone to oxygen and to convert hydrocarbons into carbon dioxide and water. The combined converters may perform both functions while also reducing weight and pressure drop when compared to separate ozone and hydrocarbon converters. Although the combined converters may reduce the odor to a significant extent, further odor reduction is desired. Increasing the amount of hydrocarbon catalyst may further reduce odor; however, the expense of the catalyst, which may comprise a precious metal, may be prohibitive.
As can be seen, there is a need for improved combined hydrocarbon and ozone converters. There is a need for an improved catalytic converter that does not increase manufacturing costs. A CHOC is needed wherein hydrocarbon conversion is increased without increasing the amount of hydrocarbon catalyst.